Inflammation is often induced by proinflammatory cytokines, such as tumor necrosis factor (TNF), interleukin (IL)-1α, IL-1β, IL-6, macrophage migration inhibitory factor (MIF), and other compounds. These proinflammatory cytokines are produced by several different cell types, most importantly immune cells (for example, monocytes, macrophages and neutrophils), but also non-immune cells such as fibroblasts, osteoblasts, smooth muscle cells, epithelial cells, and neurons. These proinflammatory cytokines contribute to various disorders during the early stages of an inflammatory cytokine cascade.
The early proinflammatory cytokines (e.g., TNF, IL-1, etc.) mediate inflammation, and induce the late release of high mobility group box 1 (HMGB1; also known as HMG-1 and HMG1), a protein that accumulates in serum and mediates delayed lethality and further induction of early proinflammatory cytokines. HMGB1 was first identified as the founding member of a family of DNA-binding proteins, termed high mobility group box (HMGB) proteins, which are critical for DNA structure and stability. It was identified as a ubiquitously expressed nuclear protein that binds double-stranded DNA without sequence specificity. The HMGB1 molecule has three domains: two DNA binding motifs termed HMGB A and HMGB B boxes, and an acidic carboxyl terminus. The two HMGB boxes are highly conserved 80 amino acid, L-shaped domains. HMG boxes are also expressed in other transcription factors including the RNA polymerase I transcription factor human upstream-binding factor and lymphoid-specific factor.
Recent evidence has implicated HMG1 as a cytokine mediator of delayed lethality in endotoxemia (Andersson, U., et al., J. Exp. Med. 192(4): 565-570 (2000)). That work demonstrated that bacterial endotoxin (lipopolysaccharide (LPS)) activates monocytes/macrophages to release HMG1 as a late response to activation, resulting in elevated serum HMG1 levels that are toxic. Antibodies against HMG1 prevent lethality of endotoxin even when antibody administration is delayed until after the early cytokine response. Like other proinflammatory cytokines, HMG1 is a potent activator of monocytes. Intratracheal application of HMG1 causes acute lung injury, and anti-HMG1 antibodies protect against endotoxin-induced lung edema (Abraham, E., et al., J. Immunol. 165: 2950-2954 (2000)). Serum HMG1 levels are elevated in critically ill patients with sepsis or hemorrhagic shock, and levels are significantly higher in non-survivors as compared to survivors.
HMG1 has also been implicated as a ligand for RAGE, a multi-ligand receptor of the immunoglobulin superfamily. RAGE is expressed on endothelial cells, smooth muscle cells, monocytes, and nerves, and ligand interaction transduces signals through MAP kinase, P21 ras, and NF-kB. The delayed kinetics of HMG1 appearance during endotoxemia makes it a potentially good therapeutic target, but little is known about the molecular basis of HMG1 signaling and toxicity.
Therefore, given the importance of HMGB proteins in mediating inflammation, it would be useful to identify antibodies that bind HMGB for diagnostic and therapeutic purposes.